This invention relates to a power converter and, in particular, to a current resonance type DC/DC multi-phase converting apparatus for combining a plurality of converter output voltages produced by a plurality of current resonance type DC/DC converters which are connected in parallel with one another and which include a plurality of resonance circuits to supply a combined voltage to a load as an output voltage and to a control method thereof.
In the manner which is well known in the art, the DC/DC converter is a power converter for converting an input DC voltage (which will later be merely also called an “input voltage”) into an output DC voltage (which will later be merely also called an “output voltage”) which is different from the input DC voltage.
As one of the DC/DC converters, there is a PWM (pulse width modulation) type DC/DC converter in the manner which will later be described in conjunction with FIG. 1.
In order to obtain high-speed, a large-capacity, a low ripple, and so on, attempt have been often made to connect a plurality of DC/DC converters in parallel with one another. On other words, there is a DC/DC converter for switching an input voltage using a plurality of switch circuits to supply an output load to a load. Such as a DC/DC converter comprising the plurality of switch circuits is called a multi-phase DC/DC converter. That is, the multi-phase DC/DC converter makes the plurality of switch circuits turn on/off at the same period and different phases to effectively enhance a switching frequency on large current output (heavy load). Such a multi-phase DC/DC converter is used, for example, as a power converter for a CPU (central processing unit).
Although a PWM type multi-phase DC/DC converter will later be described in conjunction with FIG. 2, the PWM type multi-phase DC/DC converter comprises a plurality of PWM type DC/DC converters which are connected in parallel with one another. Each PWM type DC/DC converter comprises an energizing switch. The PWM type multi-phase DC/DC converter is compatible with the high-speed and the low ripple by carrying out on-off control of energizing switches in the PWM type DC/DC converters with phases shifted.
However, the PWM type DC/DC converter is disadvantageous in that it has a large switching loss when the energizing switch changes from an on state to an off state or changes from an off state to an on state.
As a DC/DC converter which is capable of eliminating such a switching loss, a current resonance type DC/DC converter is known, for example, in U.S. Pat. No. 5,663,635 issued by Vinciarelli et al.
Although the current resonance type DC/DC converter will later be described in conjunction with FIG. 3, the current resonance type DC/DC converter includes a resonance circuit comprising a resonance inductor and a resonance capacitor. In the current resonance type DC/DC converter, a current flows through the resonance inductor only for a resonance duration with respect to a switching period. The current does not flow through the resonance inductor for a duration obtained by removing the resonance duration from the switching period. When an input/output voltage ratio becomes smaller, the switching period with respect to the resonance duration becomes longer. As a result, durations where the current does not flow through the resonance inductor increase, as described, for example, in U.S. Pat. No. 4,720,667 issued by Lee et al.
Although a conventional current resonance type multi-phase DC/DC converter will later be described in conjunction with FIG. 6, the conventional current resonance type DC/DC converter is advantageous in that it is possible to reduce the switching loss in comparison with the PWM type multi-phase DC/DC converter. Such a current resonance type multi-phase DC/DC converter is described, for example, in Japanese Unexamined Patent Publication Tokkai No. Hei 7-295662 or JP H7-295662 A. Another current resonance type multi-phase DC/DC converter having similar structure is disclosed, for example, in Japanese Unexamined Patent Publication Tokkai No. Hei 4-105552 or JP H4-105552 A.
However, it is necessary for the conventional current resonance type multi-phase DC/DC converter to prepare a plurality of resonance inductors which occupies a very large mounted area on a substrate.
Consequently, the present inventor suggested a current resonance type multi-phase DC/DC converter which is capable of reducing a mounted area on the substrate by sharing one resonance inductor in the plurality of resonance circuits.
Although the suggested current resonance type multi-phase DC/DC converter will later be described in conjunction with FIG. 7, it is possible for the suggested current resonance type multi-phase DC/DC converter to drastically reduce the mounted area of the resonance inductor which occupies on the substrate. However, in the manner which will later be described in conjunction with FIGS. 9A to 9F, the suggested current resonance type multi-phase DC/DC converter is disadvantageous in that it is difficult to have a large capacity.